1. Field of Invention
This invention relates to a piping system as encountered in a refinery or chemical plant, power plant, or buildings.
2. Description of Prior Art
The objective of this invention is to develop a design method which will arrange the shape of a piping system into the most economical system and satisfy the constraints. The most economical design in this text will be the least weight design. Since a large percentage of the cost of a refinery or chemical plant is due to the fabrication and erection of the many piping systems, a design method minimizing the weight would increase the competitiveness of the construction industry not only at the bidding stage but also at construction stage of the project.
Heretofore, the design of a refinery or chemical plant has been typically a trial and error affair. The design of the piping systems usually begins with the planning stage where the draftsman arranges the piping to satisfy the physical constraints such as support locations, interferences with equipment and existing piping, and client specifications. The initial design is then analyzed by a piping engineer using one of the numerous analytical software programs. These programs calculate the stresses in the pipe wall of the piping system and the forces and moments at the terminal points. The design constraints are dictated by industry standards such as ANSI B31.3 and ANSI B31.1 and the experience of the piping engineer. These industry standards require an analysis of the dead weight loading of the piping system to determine the stress in the pipe wall and a thermal analysis to determine the stress due to thermal expansion of the piping system. More often than not the piping system is not properly supported or has excessive thermal stress in the pipe wall so that the initial design must be rearranged by the engineer in concert with the draftsman. This iteration may be repeated numerous times before the piping system satisfies all of the design constraints and physical constraints. For a large project the manhours expended for analyzing and rearranging the piping systems can be enormous. The above synopsis assumes that the design can be brought to heel. For a cantankerous piping system, the gap between what can be done to satisfy the physical constraints and what must be done to satisfy the design constraints may be large. If the draftsman must rearrange other piping systems to accommodate this one cantankerous system, then the schedule of the project may be impaired and the judgement of the engineer questioned. The question that arises is this the only arrangement that will work? The engineer must rely largely on his experience to justify his position. What is needed, therefore, is a design method that will arrange the piping system for the least weight design and satisfy both the physical constraints and the design constraints. This would eliminate the precarious situation the engineer finds himself.
Reducing the stress in the piping system is only one piece of the puzzle for the engineer. If the piping system terminates at equipment such as a steam turbine, pump, centrifugal compressor, heat exchanger, or a tower, the manufacturer will restrict the forces and moments acting on the terminal point of the equipment. This is necessary to ensure that the equipment will operate properly in the field without excessive maintenance and costly down time. To find a solution, the piping system is rearranged and support locations moved many times in order to relieve the strain at the terminal point. This hunt and peck procedure can drag on for weeks for a large piece of machinery. The gap between what can be done to satisfy the physical constraints and what must be done to reduce the forces and moments at the terminal points begins to widen even further. What is needed is a design method which will arrange the piping system for the least weight, satisfy the physical constraints, satisfy the design constraints, and keep the forces and moments at the terminal below the manufacturers allowable.
Somewhere down the critical path, the process engineers will review the piping system for pressure drop. If the engineer has a piping arrangement that will satisfy all the above criterion, the pressure drop may be excessive. So what is needed is a design method that will arrange the piping system for least weight, satisfy the physical constraints, satisfy the design constraints, keep the forces and moments at the terminal below the manufactures allowable, and minimize the pressure drop of the system.
An engineer can not possibly keep track of all these variables without assistance from a computer-aided design method. The prior art is rich with analytical software but what is needed is a design method recommending a possible solution or more important that no piping arrangement will ever satisfy the constraints. Many hours are expended on trial and error and hunt and peck methods to find out later that the piping system will never work. But this can not be ascertained until many hours are wasted analyzing the piping system.
Many projects today are utilizing computer-aided design (CAD) to produce the drawings for construction. The software used in the shot-in-the-dark methods above require much input. Many hours are expended in modelling a complex piping system. Although much of the information needed to model a piping system is generated on the CAD system, drawings are usually produced and the engineer must glean from the drawings the input for the analytical piping software package. My invention would bypass the pick-and-shovel work of the engineer at the input stage. My invention will not reduce the amount of input to describe a piping system but will free the engineer's time for problem solving.
Since the beginning of piping analysis, many thousands if not hundreds of thousands of piping systems have been examined. Unfortunately, these successful designs have not been categorized and filed away for further use. My invention would create a data base where successful designs would be stored. The input of a new proposed piping system would be compared to this data base for a possible match. The match would not necessarily be exact, but by defining upper and lower bounds, the engineer may find a system already solved. Then applying his judgement, he could accept or reject the solved problem depending on criticality of the proposed piping system. This has the potential of saving many manhours as the data base enlarges.
Accordingly, several objects and advantages of my invention are as follows:
1. By comparing a new proposed piping system to a historical data base, the new system may be already solved saving many manhours, PA1 2. If the proposed piping system is new with regard to geometry or design conditions, then the system would be optimized and not analyzed. This would eliminate the hunt and peck systems now in use, PA1 3. By eliminating the pick-and-shove work between the CAD system and my invention, the engineer's time is freed to solve problems, PA1 4. By optimizing instead of analyzing, the engineer has a tool by which he can emphatically declare a design impracticable. This will reduce the friction between plaintiff and defendant creating a more harmonious project, PA1 5. By optimizing at the beginning of the project, the engineer can convince other engineering disciplines that changes they may make will only make the design worse, PA1 6. By exchanging data between my invention and the CAD system, the modified piping system can be checked for violated physical constraints saving many manhours, PA1 7. By using the state-of-the-art CAD systems, the draftsman may be eliminated entirely from the loop on critical systems, PA1 8. By utilizing a systems approach to a complicated design, any piping system can be analyzed.
Further objects and advantages of my invention will become apparent from consideration of the flowcharts and ensuing description of it.